"After long drive, filter gets clogged causing probably low pressure and the ECU compensates by richening fuel and causes fouling of plugs, black smoke and soot and my fuel consumption drops from 4-5km/l to 2-3km/l."


I view most of this post like the three blind men and the elephant. Each sensing a small part and drawing disasterously wrong conclusions on the whole. I'm going to leave it alone except for the above distinctly wrong evaluation.

In the above hypothesis it is claimed that the restricted fuel filter causes low pressure. I can buy that. It is then surmized that the controller will richen the mixture. I'll buy that attempt.

But the further assumption that this rich mixture fouls plugs totally misses the boat. First if the controller could control that much (which it can't) why would it take that very lean mixture through the normal mixture range to the radical rich situation that would foul plugs. Secondly and thirdly would get complicated, having to do with the concept of control when control is based on stable fuel pressure. Pretty hard to use mixture control where control is based on changing a pressure by about 3 psi when the system pressure is varying.

As for recommending system modifications by anyone not a master using full testing, I'm against it. By disabling the timing vacuum control you have no idea what you are doing. If you really wished to make a timing mod disabling the system wouldn't be the answer. The answer would be to use the provisions within the system for timing increase. That allows the system to do what its is supposed to when the pedal isn't to the metal. While full throttle might have more timing thinking it is idling, there are many times the timing would be higher if not idling. Unless you know whats supposed to happen it is not likely you are really outsmarting the system.

This post looks a lot like a little knowledge being a dangerous thing.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician